Your medium is time, you are in it and of it like a fish in water. That thing about standing on the bank and watching it flow by doesn't apply. You flow with time in a kind of ecstatic plunge. If there is something oddly unchanging about it all it is hidden away in what has been identified as retentions and protensions, or better as temporal ek-stases. These are invariant but concealed. Movement within time is the condition of experience, only what changes can be salient, but this can't come about without a fixed structure somewhere, quite heterogeneous to the freedom or unconstrainedness in every other way of what can be experienced. This unchanging element is glimpsed as structure but it is the only site in which the true subject can dwell, or rather not in it, as it.